WO 03/105324 has already made known feeding devices for feeding products and/or product stacks to a packaging process of a packaging machine, in particular a horizontal tube packaging machine, said feeding device having at least one guide unit which is realized as a closed loop along which a plurality of arranged conveyor elements are arranged so as to be drivable in a speed-controlled and/or positionally regulated manner independently of one another at least along at least one operating portion of the guide unit. The conveyor elements in each case convey one product and/or one product stack. Products are supported on one side during conveying. Support on both sides requires format parts which are adapted to a product length and have to be exchanged and/or re-arranged in the case of a change in product length.